The purpose of this study was to evaluate the efficacy of PhoSul as a phosphate fertilizer in dryland agricultural systems in the semi-arid climate of Central Montana. Total precipitation was 11.3 inches for the crop year which was around 4 inches below the 110-year average. Average annual temperature was 2.6°F higher than the 110-year mean. July was the hottest month with an average monthly temperature of 72.9°F (6.9°F above normal). Total precipitation was 0.6 in June which was only 20% of average.
A winter wheat trial was established at the MSU Central Agricultural Research Center (CARC). Treatments were compared for height, propensity to lodge, heading date, yield, test weight, and protein. Each treatment was planted in four 5 x 16 ft. plots in a randomized complete block design (RCBD) to determine differences between treatments. The study was established in a field0 that was previously planted in a lentil cover crop.
PhoSul was applied in-furrow at a rate of 75 lbs/ac. Treatments consisted of PhoSul with no starter fertilizer, PhoSul with Bacillus inoculant and 50 lb/ac 20:30:20:10 starter fertilizer, PhoSul with Bacillus inoculant and no starter fertilizer, control with 50 lb/ac 20:30:20:10 starter fertilizer and no PhoSul, and a no P control without starter fertilizer. A Bacillus inoculant was included in this study due to the putative role Bacillus plays in making P bioavailable.
The seeding date for the winter wheat study was 5 November, 2020. The planting depth was 1 inch at a rate of 60 lbs/acre. The study was sprayed with Vendetta 2 June for control of broad leaf weeds. Coated slow-release urea (46:0:0) was applied 10 June at a rate of 195 lbs/acre. Plant height and lodging scores were recorded in the field. The study was harvested 3 August 2021. Soil samples were also collected in-furrow and between rows for the PhoSul treatment, control with starter fertilizer, and the No P control to determine if PhoSul contributed to the available P. Soil samples were submitted to Ward Laboratories (Kearney, NE) for Mehlich III-P analysis. The Mehlich III test is commonly used to provide an estimate of plant available P.
Drought conditions led to below average yields for this study. Total rainfall from April-July was 5.4 inches compared to the 100-year average of 8.6 inches (Table 1). Rainfall in June, a critical month for grain fill, was 0.6 inches which is only 20% of average. Winter wheat with PhoSul alone yielded 42.7 bu/ac. This was a 36% greater yield than the control with starter fertilizer and was statistically significant at p < 0.05 (Figure 1). The remaining treatments were not significantly greater than the controls. Protein averaged 14.3% across the study and protein concentrations were not significantly different between treatments (Figure 2). Soil test results showed that available P was significantly higher (p < 0.05) in-furrow compared to between rows in PhoSul treatment and control with starter fertilizer (Figure 3). In the control with no fertilizer, there was no significant difference between P in furrow and between furrows. Complete soil test results for the field are shown in Table 2.
Although winter wheat yields were substantially lower, due to the drought, than the historic average of over 60 bu/ac, a significant treatment effect was observed in yield. Protein was variable but no significant differences were observed. This is likely due in part to the dry conditions. Slow-release nitrogen was applied 10 June, and only 0.6 inches of rain was received that month. Fertilizer granules were still visible on the ground surface at maturity.
Soil tests indicated that the PhoSul treatment had as much plant available P as controls with 50
lb/ac starter fertilizer. In both PhoSul and the control, P levels in the root zone were significantly
higher than the bulk soil between furrows. The no unfertilized control showed no significant
difference in P concentrations between in-furrow and between furrows. These results suggest
that PhoSul is capable of meeting plant P requirements. Given that P concentrations were
virtually identical between PhoSul and the control, it seems unlikely that the yield increase with
PhoSul was a P response. PhoSul also contains S and amorphous silica, and it is possible that one
of these components contributed to the yield response.